Production of unsaturated hydrocarbons



1959 E. M. HUGHES ET AL PRODUCTION OF UNSATURATED HYDROCARBONS Filed Aug. 29, 1955 M 2M n ws m mp I a m4 1 M wt H4 u l h. M G EAOI.

Attorneys.

United States Patent PRODUCTION OF UNSATURATED HYDROCARBONS Edward Morgan Hughes, Alfred Harold Howland, and Pieter Grootenhuis, London, England, assignors to National Research Development Corporation, London, England, a British company Application August 29, 1955, Serial No. 530,942

Claims priority, application Great Britain September 3, 1954 Claims. (Cl. 260-679) It has been shown in British patent specification No. 711,208 that the process of production of acetylene and other unsaturated hydrocarbons, among which may be mentioned ethylene, by cooling the gaseous reaction products resulting from the partial combustion of a hydrocarbon fuel with air or oxygen under such conditions as to produce pyrolysis and/or cracking of excess hydrocarbon is improved considerably if the said cooling is effected by expanding the gaseous reaction products adiabatically in a gas turbine in which they perform mechanical work.

It is an object of the present invention to provide an improved apparatus for the process of production of acetylene or other unsaturated hydrocarbon using a gas turbine as aforesaid.

The requirements of the process are that the hydrocarbon fuel and the oxidant shall be separately preheated and then be reacted together in a combustion chamber, there being a considerable excess of the hydrocarbon over that required forcomplete combustion with the air or oxygen; the heat of combustion then causes pyrolysis or cracking of the excess hydrocarbon fuel. The gases must be allowed to reside at this high temperature for a short, but precisely defined, interval of time, which may be termed the residence time, and-then cooled as rapidly as practicable to a temperature not greater than 200 C. All or part of this cooling may be done in a gas turbine.

It follows that the requirements of the combustion chamber used for the combustion are as follows:

(1) It should be capable of burning stably the very rich mixtures required.

(2) The combustion must take place in a very short space of time.

(3) The burner must operate stably with preheated supplies of hydrocarbon fuel and oxygen.

(4) The heat-loss during the residence time must be small.

(5) The rate of throughput of gas must be sufficiently high to satisfy the turbines requirements.

(6) The combustion must be stable when the combustion chamber is operating under pressure, and under fluctuations of pressure.

Attempts to meet requirement (2) above have been made by employing a burner in which the reactants are mixed before entering the combustion chamber. This,

however, imposes a restriction on the degree of preheating that is feasible, also decreases stability, particularly under fluctuations of pressure.

In accordance with the present invention there is provided an apparatus for producing acetylene and other unsaturated hydrocarbons by subjecting liquid or gaseous hydrocarbon fuel to incomplete combustion with air or oxygen under such conditions of temperature as will cause cracking and/or pyrolysis of the excess hydrocarbon fuel and subjecting the combustion products to rapid cooling, which apparatus comprises a combustion chamber, a fuel nozzle for projecting a jet of hydrocarbon fuel ranged for obstructing the jet and thereby spreading the hydrocarbon fuel in a thin sheet, distributor means for supplying air or oxygen to the thin sheet tor combustion thereof and combustion products withdrawal means for withdrawing combustion products from the combustion chamber.

tor the production of acetylene, a rapid quenching of the combustion products is required and to effect this rapid quenching it is preferred that there is connected to the combustion chamber a gas turbine in which the combustion products may be subjected to adiabatic expansion to produce the required rapid cooling thereof.

in a convenient arrangement, the distributor means for supplying air or oxygen to the thin sheet of hydrocarbon ruel comprises a plurality of inlet ports formed through the wall of the combustion chamber at positions distributed around the nozzle, said ports being in commumcation with a manifold arranged outside the chamber. "lhe axesbf the ports may be parallel with that of Q the nozzle or may be inclined slightly inwardly thereto.

A single annular inlet port may be used if desired.

The distributor means may, if desired, be so designed as to feedthe whole or a part of the air or oxygen through or around the obstructing element. "thus the distributor means may comprise, tor example, a plurality of ports formed through the obstructing element or an annular port surrounding the obstructing element. Furthermore, the obstructing element or'a part thereof may be made of porous material and be so arranged that the air or oxygen or part thereof may be fed therethrough; the obstiucting element itself may thus form a part of the distributor means.

"the combustion chamber is preferably an axially short cylindrical combustion chamber substantially on the axis of which are mounted the fuel nozzle and the obstructing' element.

The combustion products withdrawal means. preferably comprises a continuous or discontinuous outlet aperture which surrounds the obstructing element and which cornmunlcates from within the combustion chamber to a combustion products manifold. Such an outletaperture may, for example, be provided in the form of a plurality of outlet ports or a single port of annular form formed in the wall of the chamber.

When there is employed, as the cooling means for the combustion products, an axial flow gas turbine, the combustion products manifold is conveniently of annular cross-section, the major cross-sectional dimensions thereof being reduced between the outlet aperture and the outlet nozzle to provide a converging pathway for the combustion products. In a preferred arrangement, this manifold is provided in the form of a space defined between a conical body and a conical elongation of the combustion chamber itself in which case the obstructing element may be provided inthe form of a cylindrical pro ection formed substantially at the centre of the base of the conical-body. I

The rapid and eliieient mixing of the hydrocarbon'and the oxygen-containing gas obtainable within the combustion chamber completely dispenses with any need-to premix these materials. The apparatus may therefore be provided With a preheater for one or both of these materials thereby increasing the efiiciency of the reaction while avoiding the danger that the materials will ignite before reaching the combustion chamber, or that the combustion will be unstable even under conditions where the velocity of flame propagation is lower than the velocity of the difierent gases. The only limits imposed on the preheat temperature arise from the economic considerations of the process as a whole and from the.

possibility of the hydrocarbon fuel being cracked in the preheater.

The combustion chamber and the obstructing element may be made ot a snitable reiractory material, a refractory-lined metal, or of a metal. suitably cooled, one form of. such, cooling being by heataexchange with one or both oithev reactants toconserve heat.

Itis. a feature of the Combustion chamber that it provides very great stability over a wide, range of mixture ratios and, pressures. For instance, propane and air have been burnt in the ratio 1:120 by volume on the weak limit, and 1:1.45 on the rich limit. Operating on methane and oxygen it is entirely stable over the range of me hane/oxygen ratios 2.61:1 to 1.3:1 by volume, his being the range in which it is likely to be required to. operate for the hydrocarbon cracking process in the gas turbine. The combustion chamber has been shown to operate stably over this range up to pressures of 5 atmospheres. Molecular oxygen fed into the combustion chamber may be. sufficient to combust only a part of the hydrocarbon. I

The invention also includes a process for the production of unsaturated hydrocarbons from saturated hydro carbons by the pyrolysis or cracking of saturated hydrocarbons by partial combustion in the apparatus herein described.

The. invention will be further understood from the following description of two preferred embodiments of the apparatus in which description, reference is made to the accompanying drawings of which:

, Figure l shows in longitudinal cross-section a combustion chamber arranged for use with a radial flow gas turbine,

Figure 2 shows, a longitudinal cross-section of a combustion chamber arranged for use with an axial flow gas turbine.

a cylindrical obstructing element 6. A plurality of inlet ports 7 formed through wall 1. at positions. surrounding fuel pipe and, in such directions as to be convergent to the axis of the chamber, serve for distributing an oxygencontaining gas, supplied to manifold 8 by pipe 9, to the thin, sheet of fuel formed by the jet of fuel issuing from the nozzle 5. and impinging upon the obstructing element 6. A discontinuous outlet aperture in the form of a plurality of radial outlet holes 10 communicates with a combustion products manifold. 11 constituted by the tube 3,. a tube 12 arranged coaxially therewith, and annular end plates 13 and 14. A pipe 15 serves for loading combustion products from the manifold, to a radial-flow gas turbine, shown diagrammatically at T.

In. th app rat s; sh wn. in Figure 2,. a combustion chamber 29 having a cylindrical portion 21 and, a coaxial conical por ion 22. ha ing p si oned therein a conical body 23 which cooperates to define a continuous outlet aperture 24 and a, converging combustion products manifold. 25which, connects aperture 24 with an outlet nozzle 26 which communicates with an axial, flow gas turbine, shown diagrammatically at; 27. Parts 4, 5, 6, 8 and 9 are imil r to the correspondingly numbered parts of the apparatus shown in Figure 1.

For the partial combustion method of pyrolysing or cracking hydrocarbons, it has been shown that the combustion products formed in the combustion chambers of Figures 1 and 2 contain satisfactory amounts of unsaturated hydrocarbons. For example an apparatus substantially as shown. in Figure 1, running on propane/oxygen in the ratio 09:1 by volume, produced, without preheat, a yield of 9% acetylene in a test run, employing water quenching, together with a similar amount of ethylene. An apparatus substantially as shown in Figure 2, running on methane/oxygen in the ratio 1.65:1 by volume produced under similar conditions 3.4% acetylene.

The residence time of the reacting mixture to give appreciable yields of acetylene was found to be from 20 to milliseconds, this residence time being based on the time taken by the mixture to traverse the combustion chamber when at atmospheric temperature and pressure.

It will be understood that although for convenience herein, the nozzle directed at the obstructing element is referred to. as a fuel nozzle and although the distributor means is stated to have the function of supplying, air or oxygen to the thin sheet, the functions of these two structural elements may be reversed. Thus the apparatus may successfully be used with air or oxygen supplied to. the nozzle and spread out into a thin sheet to which the fuel is supplied by the said distributor means.

What is claimed is:

1. A process for the conversion of substantially saturrated. hydrocarbons to substantially unsaturated hydrocarbons which comprises introducing the saturated hydrocarbon into a closed. combustionv chamber in the. form. of a jet, forming a thin sheet of radially moving hydro,- carhon within the combustion chamber by impinging, said iet upon an obstructing; element disposed within said chamber, separately introducing. molecular oxygen into said combustion chamber annularly of said jet, etfecting a, partial combustion of said hydrocarbon, withdrawing the. combustion products from said combustion chamber. and quenching them.

2. A process according to claim 1 wherein the hot come bustion products.- are: withdrawn from said combustion chamber and directly quenched byadiabatic expansion in a gas turbine.

3. A process according. to claim, 2 wherein the residence time of the reactants in said combustion chamber is from 20 to 50 milliseconds.

4. A process according, to. claim 3 wherein the, reactants are preheated. before introduction. into the com bustion chamber.

5. A process according; to claim 1 wherein the amount of molecular oxygen fed into the combustion chamber, issufiicient to-combust only part of, the hydrocarbon.

. References ited in the tile of this patent;

UNITED STATES PATENTS Pichler et a1. Oct. 2, 1956' 

1. A PROCESS FOR THE CONVERSION OF SUBSTANTIALLY SATURATED HYDROCARBONS TO SUBSTANTIALLY UNSATURATED HYDROCARBONS WHICH COMPRISES INTRODUCING THE SATURATED HYOF A JET, FORMING A THIN SHEET OF RADIALLY MOVING HYDROCARBON WITHIN THE COMBUSTION CHAMBER BY IMPINGING SAID JET UPON AN OBSTRUCTING ELEMENT DISPOSED WITHIN SAID CHAMBER, SEPARATELY INTRODUCING MOLECULAR OXYGEN INTO SAID COMBUSTION CHAMBER ANNULARLY OF SAID-JET,EFFECTING THE COMBUSTION PRODUCTS FROM SAID COMBUSTION CHAMBER AND QUENCHING THEM. 